Method for producing a cup-shaped object

ABSTRACT

A method for the production of a cup-shaped article, in particular a blank of a screw cap for glass bottles or the like, from an enameled metal sheet, using two tools in a stepwise manner: 1) the blank is stamped from the metal sheet in a first tool by the relative motion between a cutting bell cooperating with a blank holder and a drawing block, and the blank is drawn around the drawing block, the width of a flange forming between the cutting bell and the blank holder being continuously reduced with a progressive degree of deformation until the flange reaches a defined width (R-r), and 2) the blank is deformed in a second tool such that the radially outwardly directed flange is deflected toward a profiling introduced in a wall of the blank.

FIELD OF INVENTION

The invention relates to a method for the stepwise production of acup-shaped article, in particular a blank of a screw cap for glassbottles or the like, from an enameled metal sheet, whereby in a firststep the blank is stamped from the metal sheet by deep-drawing based onthe relative motion between a cutting bell cooperating with a blankholder and a drawing block, and the blank is drawn around the drawingblock, the width of a flange of the blank forming between the cuttingbell and the blank holder being continuously reduced with a progressivedegree of deformation.

BACKGROUND DESCRIPTION

Deep drawing is understood to mean the shaping of a sheet metal section(circular blank, plate blank) into a hollow body, or the shaping of ahollow body into a hollow body with a smaller circumference, with orwithout intentional modification of the sheet metal thickness. Duringshaping, segments of the blank must be folded up on the cylinder wall,with the parts inbetween being displaced, thus creating radial tensileand tangential compressive stresses. Bending occurs when the cuttingbell runs over the blank. The blank holder impinged on by force isprovided to prevent the radially outwardly projecting flange frombuckling and forming folds under the influence of the tangentialcompressive stresses.

The caps provided for glass bottles are drawn from relatively thin metalsheets. These sheets, in particular when used in the food industry, areenameled and in many cases have commercial printing. A problem with thecap manufacture is that during shaping in the axially outer region ofthe cup the enameling cracks and forms fine colored filaments. Thecracked enameling does not detract from the appearance, since the axialend of the blank is subsequently rolled in so that the crackedlocations, which are also very fine, are not visible on the finishedproduct. However, the colored filaments become lodged not only in thetools but also on the edge of the blank, and a cotton-like texture formsin the tools which must be regularly removed. In addition, the filamentsthat remain on the cup, in particular on the edge thereof, must becarefully removed so that during filling they do not come into contactwith the filling material (foodstuffs), which would be unacceptable.

Caps for glass bottles are mass-produced articles which are manufacturedin large quantities in a tool with high cycling times. The cycling timestypically have values of approximately 300 min⁻¹. To remove thefilaments, the manufacturing unit containing the tool must be shut downand blown out or cleaned, thereby lengthening the production time andalso increasing the manufacturing costs. The filaments must be blown outvery carefully so that the operators of the unit are not subjected tohealth risks. In addition, the room in which the units are set up mustbe continually cleaned to remove the colored filaments.

Various methods having stepwise deformation have been developed in theprior art. DD 233 036 A3 discloses a method for deep-drawing sheet metalparts in which a first draw is followed by a second draw within the samepress stroke in the same direction, the drawing force of the first drawbeing employed as a hold-down force by the second draw and being reducedwith progressive drawing depth. The hold-down force is progressivelyreduced from the start of the second draw, and is entirely eliminatedbefore the shaping in the second draw is completed.

In addition, a drawing method for a disk-like metal sheet is known fromDE 692 06 748 T2 in which an annular holding element and/or the drawingtool, which have a residual flange region, are moved in such a way thatthe holding operation is terminated immediately before the drawing stageis completed. The flange region is then drawn while the back end of theflange region is released.

Both methods share the common feature that they are each carried out ina single tool, so that the shaped part remains in this tool during thestepwise deformation. In practical operation, in particular for highcycling times, release of the hold-down force cannot be reliablyensured. For example, for a pneumatically operated unit the responsetime for the control is too slow to maintain the high cycling time. Forthis reason, filament or tail formation cannot be ruled out, even duringthe second process step when the blank holder should not exert any forceon the blank to be deformed.

SUMMARY OF THE INVENTION

Proceeding from this problem, the object is to improve the methodexplained at the outset in such a way that, in particular for highcycling times, filament or tail formation is greatly reduced or evencompletely eliminated.

This is attained by a method according to the invention in which theproduction takes place in two tools in a stepwise manner:

-   -   1) The blank is stamped from the metal sheet in a first tool by        the relative motion between a cutting bell cooperating with a        blank holder and a drawing block, and the blank is drawn around        the drawing block with impingement of force on the blank holder,        the width of a flange forming between the cutting bell and the        blank holder being continuously reduced with a progressive        degree of deformation until the flange has reached a defined        width,    -   2) The blank is deformed in a second tool so that the radially        outwardly directed flange is deflected toward a profiling        introduced in a wall of the blank.

The invention is based on the finding that the filament formationresults not from the high cutting forces during stamping of the circularblank from the metal sheet, as might be assumed, but rather from thevery high surface pressure on the flange, which is formed between thecutting bell and the blank holder, at the end of the deep drawing. Dueto the defined width of the flange, the deep drawing or deformation isinterrupted shortly before the surface pressure in this flange reacheslevels which cause the enamel layer to crack. The cracking of the enamellayer on account of the excessive surface pressure would cause theenamel layer to draw filaments.

The flange then has a maximum width of, e.g., 3 mm, which is very smallcompared to the height of the cup. The flange is deformed or deflectedin a second step in a second tool, without impingement of force on ablank holder, so that no surface pressure acts on the flange duringdeflection. The necessary shaping force may be kept very low due to theonly slight degree of shaping required, thus preventing cracking of theenamel layer and formation of filaments. Introduction of a profiling inthe wall of the blank provided in the second step prepares the blank forfurther processing, such as curling the wall inward.

This method eliminates the shutdown time heretofore necessary forcleaning, and the associated costs, which significantly reduces themanufacturing costs. Since there are no filaments on the blank either,the additional work step and corresponding control steps previouslyrequired for removing the filaments are also omitted, which furtherlowers the manufacturing costs. In addition, tail formation is reduced.Besides the reduction in manufacturing costs, the quality of the productis increased.

An advantageous embodiment of the inventive concept provides that thedeformation is carried out by drawing out the flange based on therelative motion between a cutting bell and a drawing block of the secondtool.

An alternative embodiment of the method according to the inventionprovides that the deformation is performed by a guide which cooperateswith the second tool. Lastly, a further alternative embodiment of themethod according to the invention provides that the deformation iscarried out by rolling in a second tool. The rolling renders possible asimple and efficient shaping method in order to prepare the blank forfurther processing.

The wall preferably is drawn radially outward by the profiling.Alternatively, the profiling causes the wall to deform facing radiallyinward. These embodiments of the profiling prevent folds or buckles fromforming in the wall during a subsequent curling of the wall, whichincreases the quality of the finished cap. In addition, there is no needto tilt or slide the cap forward later in order to curl the edge.

The radial width of the flange at the end of the first shaping step isless than 3 mm, preferably 0.1-1.5 mm, particularly preferably 0.5-1.0mm. The smaller the width of the flange, the less force is needed forshaping in the second step. Of course, the width of the flange dependson the surface pressure present, which in turn depends on the materialas well as the material thickness or sheet thickness and the compatiblemaximum value thereof in correlation with the thickness of the coloredlayer. The optimum width of the flange is iteratively determined in eachcase for various basic conditions, such as the material, materialthickness, and the colored or enameled layer.

DESCRIPTION OF DRAWINGS

The method according to the invention is explained in greater detail byway of example, with reference to the accompanying drawings. They show:

FIG. 1 A partial half section of a first deep-drawing tool;

FIG. 2 A deep-drawing tool in partial half section according to theprior art;

FIG. 3 A first deep-drawing tool in partial half section for carryingout the method according to the invention at the end of the firstsubstep;

FIG. 4 A second deep-drawing tool in partial half section at the end ofthe second substep;

FIG. 5 A further second deep-drawing tool for carrying out the methodaccording to the invention at the end of the second substep, in partialhalf section;

FIG. 6 The diagrammatic representation for further processing of theblank produced according to the invention;

FIG. 7 a An alternative shaping tool for carrying out the methodaccording to the invention at the start of the second substep, inpartial half section;

FIG. 7 b The shaping tool according to FIG. 7 a at the end of the secondsubstep;

FIG. 8 A top view of the shaping tool from FIG. 7 for carrying out themethod according to the invention for the second substep, in partialhalf section;

FIG. 9 A top view of an alternative shaping tool for carrying out themethod according to the invention for the second substep, in partialhalf section.

Identical or equivalent components are provided with the same referencenumbers in the figures.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 shows a partial section of the first deep-drawing tool,symmetrically structured about the centerline M, comprising the cuttingring 1, the cutting bell 2, the blank holder 3 which cooperates with thecutting bell 2, the base 4 which supports the drawing block 6, and thestamping block 7. The stamping block 7 and the drawing block 6 togetherwith the cutting bell 2 enclose the blank 8. The force from a springassembly (not illustrated here in greater detail) is transmitted to theblank holder 3 via hold-down pins 5 arranged uniformly distributed on aperipheral circle.

The blank 8 is produced according to the prior art using the toolaccording to FIG. 2, the enameled metal sheet or circular blank cut(stamped) therefrom by the cutting ring 1 being placed on the drawingblock 6. The stamping block 7 and the cutting bell 2 are lowered ontothe metal sheet, whereby the cutting bell 2 stamps a sheet metal platefrom the circular blank. After the metal sheet is separated, a flange ispinched between the blank holder 3 and the cutting bell 2, the width ofwhich flange is continuously reduced in a further lowering motion of thecutting bell 2 and blank holder 3. The reduction in the width of theflange causes the surface pressure in the flange to increase as theresult of the force F acting on the blank holder 3.

FIG. 3 shows the first tool at the end of the first substep of themethod according to the invention. The cutting bell 2 and the blankholder 3 are jointly moved in relation to the drawing block 6 until adefined surface pressure develops in the flange 8 a of the blank 8,i.e., until the width of the flange 8 a formed by the difference betweenthe outer radius R and the inner radius r has reached a defineddimension. This defined dimension is less than 3 mm, preferably 0.1-1.5mm, particularly preferably 0.5-1.0 mm. This dimension is thus verysmall compared to the inner radius r of the blank 8.

The two steps of the deep-drawing method according to the invention arecarried out in two different tools. Thus, a conventional first tool maybe used in which the blank holder 3 is acted on by force, e.g., via aspring assembly. After the first step is completed, the blank 8 isremoved from the first tool and inserted into a different, second toolwhich either has no blank holder 3, as shown in FIG. 5, or has a blankholder 3 which exerts no force, as shown in FIG. 4.

In the second step shown, e.g., in FIG. 4, in a second tool, the blankholder 3 exerts no force in the deformation, and the cutting bell 42shapes the blank 8 in a further deep-drawing step. A radially outwardlydirected profiling 8 c is thus introduced at the axial outer end of thewall 8 b, which profiling 8 c ensures in the subsequent curling of thewall 8 b that no folds or buckles develop in the wall 8 b. The interiorof the cutting bell 42 and the exterior of the drawing block 46 have ashape that corresponds to the profiling 8 c. In the illustrated tool,the blank holder 3 shown in FIG. 4 is used only as a lifter, which thenejects the shaped part upwardly from the tool by a lifting motion afterthe deformation is completed.

An alternative second tool illustrated with reference to FIG. 5 differsfrom the tool shown in FIG. 4 in that a blank holder is omittedaltogether. An ejecting element 9, integrated into the drawing block 56as a lifter, is provided instead for lifting or releasing the shapedpart, and ejects the shaped part upwardly from the tool by a liftingmotion after the deformation is completed. It is also possible toprovide an air channel in the drawing block 56 to release the shapedpart from the drawing block 56 by an air blast and eject it from thetool.

Curling of the wall 8 b is shown in FIG. 6. The radially inward rollingoffsets the radially outwardly directed profiling 8 c, which causes thewall 8 b to assume a linear course. The slightly flanged edge is thenfurther curled to increase the stability of the cap. For a screw cap,after the curling is completed, lobes 8 d uniformly distributed over thecircumference are pressed in at the lower edge, which lobes latercooperate with the thread applied to the neck of the glass bottle.

An alternative deformation of the blank 8 in the second substep of theinvention is explained below, with reference to FIGS. 7 a and 7 b. Theblank 8 shaped in the first substep (see FIG. 3) has a radiallyoutwardly directed flange 8 a in the lower region of the wall 8 b, andis placed on a shaping block 10. The shaping block 10 has a shoulder 11on its outer circumference such that the diameter in the lower region 10a of the shaping block 10 is smaller than the diameter in the upperregion 10 b. In addition, the shoulder 11 is located essentially in theregion of, or at the height of, the flange 8 a of the blank 8 when theblank is placed on the shaping block 10.

In the deformation presented here, a roller 12 approaches the flange 8 aof the blank 8 from the outside. The arrow 13 indicates the direction ofmotion of this approach. The roller 12 rotates about its longitudinalaxis 14, which is inwardly inclined at the level of the flange 8 a. Inother words, the lower region of the roller is closer to the shapingblock 10 than is the upper region. The rotation about the longitudinalaxis 14 is indicated by the curved arrow 15. The roller 12 is guidedfarther inward until the blank 8 is deflected in the lower region havingthe flange 8 a, so that a profiling 8 e directed radially inward isformed in the wall 8 b, as shown in FIG. 7 b. A relative motion betweenthe roller 12 and the shaping block 10 together with the blank 8thereon, for example, a rotation of the shaping block 10 about itscenter axis, shapes the profiling 8 e radially inward along the entireouter circumference of the wall 8 b of the blank 8.

To allow the blank 8 to be removed or lifted from the shaping block 10,the wall 8 b together with the profiling 8 e must be moved radiallyoutward during the upward removal until the inner edge of the profiling8 e can be guided past the shoulder 11. It is expedient for thedimensions of the shoulder 11 or the profiling 8 e to be selected suchthat this deflection remains in the elastic deformation region of theblank 8. After removal, the wall 8 b then springs back to the shapeproduced by the deformation in the second substep.

However, it is also possible for the deflection not to be purelyelastic, but rather to be associated with a plastic deformation as well.In that case, however, the dimensions of the shoulder 11 and theprofiling 8 e should be selected such that after the elastic portion ofthe deflection has returned, the profiling 8 e is still embodied to bedirected sufficiently radially inward. In other words, in this caserolling causes the profiling 8 e to be inwardly deformed more than isnecessary for further processing.

FIG. 8 diagrammatically shows a top view of an apparatus 16 having theshaping tool from FIGS. 7 a and 7 b. In this example, the apparatus 16has a total number of eight shaping stations 17 which are situatedequidistantly from one another on a circle (indicated by a dashed-dottedline) and which rotate about the center of this circle. Of the eightshaping stations 17, the figure illustrates only the three that areengaged. Each shaping station 17 has a shaping block 10 upon which ablank 8 may be placed. Each shaping station 17 also has a roller 12which is held by a support arm arrangement 18.

In the illustration in FIG. 8, the blank 8 is supplied to the apparatus16 from the left and is arranged on the rotating shaping block 10. Theblank 8 is shaped by rolling while the apparatus 16 together with allthe associated shaping stations 17 rotates in the counterclockwisedirection. After a partial rotation of the apparatus 16 by approximately180°, the blank 8 exits the apparatus 16 to the right in theillustration according to FIG. 8. In the next partial rotation, theshaping block 10 remains unoccupied until it is once again provided witha new blank 8 on the left side of the illustration. During deformationthe shaping block 10 occupied by a blank 8 is rotated about itslongitudinal axis, which is perpendicular to the plane of the drawing.In this manner the blank 8 is provided with the profiling according tothe invention along its entire outer circumference. By way ofclarification, the figure respectively shows a cross section through theblank 8′ before shaping and through the blank 8″ after shaping.

Lastly, FIG. 9 shows a further apparatus 19 for carrying out thedeformation according to the invention in the second substep. Theapparatus has a total number of eight shaping blocks 10 which arearranged equidistantly from one another on a circle and which rotateabout their common center axis in the counterclockwise direction.Furthermore, each shaping block 10 also rotates about its longitudinalaxis, which is perpendicular to the plane of the drawing. As with theapparatus 16 already illustrated in FIG. 8, the blank 8 is likewisesupplied to the apparatus 19 from the left side (based on theillustration in the drawing) and is discharged from it after theapparatus 19 has made a partial rotation of approximately 180°.

During the partial rotation, the blank together with the flange 8 alocated on the wall 8 b is brought into contact with an inner surface 20of a rigid guide 21 which has essentially a semicircular shape. It isnot clearly shown in the figure that the radius of the semicircle tapersin order to continuously further deform the blank 8 in contact with theinner surface 20, so that the blank has an inwardly directed profiling 8e when discharged from the apparatus 19, as is also produced by theapparatus shown in FIG. 8.

For the deformations in the second substep presented here, all of thealternative procedures share the common feature that the deforming forceis not opposed by a force or counterforce applied to the blank 8 fromoutside. The cutting bell 2 exerts only a downward perpendicular forceon the blank 8 during the drawing (see FIGS. 4 and 5). For thedeformation by a roller 12 or a guide 21 (see FIGS. 8 and 9), the blank8 is acted on only by a force from radially outward and downward. Acounterforce, such as that exerted by the blank holder in the firstsubstep, does not act on the blank in the second substep.

1. A method for the production of a cup-shaped article, from an enameledmetal sheet, stepwise in two tools comprising: stamping a blank from themetal sheet in a first tool by a relative motion between a cutting bellcooperating with a blank holder and a drawing block, and the blank isdrawn around the drawing block with impingement of force on the blankholder, a width of a flange forming between the cutting bell and theblank holder being continuously reduced with a progressive degree ofdeformation until the flange has reached a defined width R-r while stillremaining pinched between the cuffing bell and blank holder, wherein Ris an outer radius of the blank including the flange and r is an innerradius of the blank which does not include the flange, and deforming theblank in a second tool without impingement of force on any blank holderacting on the flange while the flange is deflected toward a profilingintroduced in a wall of the blank, wherein the radial width R-r of theflange is essentially less than 3 millimeters.
 2. The method accordingto claim 1, wherein the radial width R-r is 0.1-1.5 mm.
 3. The methodaccording to claim 2, wherein the radial width R-r is 0.5-1.0 mm.